1. Technical Field
This invention relates in general to hard disk drives and in particular to enhanced mechanical features on hard disk drive actuator pivot cartridges including contact pads that are axially inboard of the pivot bearings and a pivot sleeve with an enhanced wall thickness for improving the servo stability of the disk drive.
2. Background Art
Referring to FIG. 1, a conventional, prior art actuator pivot cartridge 11 for a hard disk drive has an outer, cylindrical housing or sleeve 13 with a bore 12 and axis 14, an inner pivot shaft 15, and a pair of bearings 17. Shaft 15 rotates or pivots relative to sleeve and bearings 17 are mounted in counterbores 18 at the axial ends of sleeve 13. Counterbores 18 have a larger diameter than that of bore 12. Note that counterbores 18 only support the outer races of bearings 17 and that bore 12 is located radially outward of the center of the balls of bearings 17. Sleeve 13 has a threaded radial mounting hole 23 that is centrally located between its axial ends.
Sleeve 13 also has a wall thickness 19 of approximately 2.0 mm. Thickness 19 is adequately sized to generally handle most loads exerted on cartridge 11. However, thickness 19 is less than twice as thick as the wall thickness of the sleeve at counterbores 18. Wall thickness 19 also provides ample clearance (about 1.0 mm) between bore 12 and the outer surface of shaft 15. The external profile or cross-section of sleeve 13 is altered slightly at its axial ends with integrally formed, annular bosses or pads 21 that extend around its circumference. Pads 21 are provided as closely toleranced, highly repeatable contact surfaces for cartridges 11 as will be described below. If cartridge 11 had a smooth cylindrical exterior along its entire axial length, the tolerances of the contacting surfaces would be much more difficult to control. Pads 21 are substantially axially aligned with their respective bearings 17 and counterbores 18.
A second prior art example is illustrated in FIG. 1A as cartridge 11A. This example is more fully described in U.S. Pat. No. 5,446,608. Like cartridge 11, cartridge 11A has a sleeve 13A with a bore 12A and axis 14A, a shaft, and a pair of bearings 17A in counterbores 18A. Sleeve 13A has a conventional wall thickness 19A of approximately 2.0 mm. Cartridge 11A also has a pair of narrow pads 21A that are located axially outward or xe2x80x9coutboardxe2x80x9d of bearings 17A.
As shown in FIGS. 2 and 3, cartridge 11 or 11A (only cartridge 11 is shown for simplicity) mounts in the cylindrical bore 25 of an actuator comb 27. A scallop-shaped, undercut portion 29 extends axially along the inner surface of bore 25 for providing two axial xe2x80x9clinesxe2x80x9d of contact 30 for cartridge 11. Cartridge 11 is secured from movement relative to comb 27 with a single screw 31 that extends through a radial hole in comb 27 into the undercut portion 29. The outer surfaces of pads 21 make contact with lines 30 in bore 25 (FIG. 4). Due to the axial end positions of pads 21 and the limited wall thickness 19 of sleeve 13, cartridge 11 tends to bow slightly along axis 14 and distorts radially to form an ellipse (shown exaggerated for ease of understanding). Even a slight axial or radial distortion in cartridge 11 will decrease the servo stability, decrease servo performance, and increase the torsional resistance of bearings 17 due to the changes in bearing stiffness.
A disk drive with poor servo stability will generate an excess of hard errors. Instability can be characterized by measuring the plant transfer function of the drive and examining the relevant dynamic modes. Modes which are not at the proper gain or frequency are the sources of the instability. For example, at the xe2x80x9cbutterflyxe2x80x9d mode (FIG. 5), the heads 33 of the drive oscillate over the midpoint 35 of the unit in a uniform pattern. In the S-mode (FIG. 6), the top, middle and bottom heads 37 oscillate about the midpoint 35 by a small amount, while the remaining heads 39 oscillate with greater magnitude.
The S-mode can be filtered out using a servo notch if it remains at a consistent frequency and gain. However, if the mode has a large gain or spread, or it is located at a frequency outside the servo notch zone, the mode will remain unfiltered and cause servo instability. These modes are very sensitive to the stiffness of the actuator mechanical system components, including the pivot cartridge, actuator comb, coil, head gimbal assembly (HGA), and their interfaces. Thus, an improved mechanical system with greater component stiffness is desirable to increase servo stability and performance of the disk drive.
A hard disk drive actuator pivot cartridge has a sleeve, a coaxial pivot shaft, and a pair of bearings therebetween. The bearings are located near the axial ends of the shaft. The sleeve has a wall thickness that is substantially greater than those of prior art sleeves. The sleeve also has a pair of annular pads that are located axially inward of the bearings. The cartridge mounts inside an actuator comb such that only the pads contact the bore of the comb. The axial location of the pads and the greater wall thickness of the sleeve significantly decrease the bending experienced by the cartridge when it is installed in the comb, and thereby increase the servo stability and performance of the disk drive.